Proteins play a central role in all biological processes. Akin to the complete sequencing of genomes, complete description of protein structures is a fundamental step towards understanding biological life, and is also highly relevant medically in the development of therapeutics and drugs. The broad, long-term goal of the project is to develop machine learning methods for data-driven protein structure prediction through two independent but complementary strategies: 1) much more accurate template-based modeling for proteins with remote homologs in the Protein Data Bank and 2) better template-free modeling method for proteins without detectable templates and for improving template-based models. The specific aims are: Aim 1) to greatly improve template-based modeling by 1a) improving protein sequence-template alignment using a regression-tree-based nonlinear scoring function, especially when good sequence profiles are unavailable; and 1b) improving fold recognition using a machine learning method to combine both residue-level and atom-level features; Aim 2) to improve protein conformation sampling in a continuous space and thus template-free modeling by three independent but complementary approaches: 2a) modeling nonlinear sequence- structure relationship using Conditional (Markov) Random Fields (CRF) models; 2b) simultaneously sampling secondary and tertiary structure; and 2c) learning structure information from template. The core of the project is to develop various CRF models for data-driven protein structure prediction, by learning protein sequence-structure relationship from existing sequence/structure databases. The product of this research includes a regression-tree-based CRF model for accurate protein alignment, especially for proteins without close homologs in the PDB or without very good sequence profiles; a SVM model for protein fold recognition; a few CRF models for efficient protein conformation sampling in a continuous space; and a complete protein structure prediction software package. Also, it will produce a web server publicly available for various academic and biomedical users. Protein structure prediction will lead to a broad range of biomedical applications, such as the development of novel diagnostics, better understanding of disease processes and improved preventive therapies leading to reduced health care costs. Protein modeling is also widely applied in the pharmaceutical industry and integrated into most stages of pharmaceutical research.